This invention relates to techniques for growing films, particularly diamond films, on foreign substrates, and the films and products prepared from such techniques.
Thin films of diamond are known to have great potential for use in a variety of applications due to their exceptional mechanical, thermal, optical and electronic properties. For example, diamond films can be used as semiconductors, transitors, heat sinks, optical coatings, optical devices, electronic devices, as coatings for drill bits and cutting tools, and as inert coatings for prosthetics. Unfortunately, as presently deposited by known techniques on nondiamond (foreign) substrates, diamond films are characterized by highly disordered polycrystalline structures which can cause them to be incompatible with many prospective applications. For applications to electronic devices where semiconducting diamond films on foreign substrates such as silicon could offer extraordinary advantages, the problems are particularly serious. Unless microstructure and morphology are substantially improved, it may be difficult or impossible to utilize polycrystalline diamond films in practical electronic devices.
A major factor involved with the disordered microstructure of conventional diamond films grown on nondiamond substrates is that such films are characterized by very low nucleation densities. For example, the nucleation density when diamond is deposited on a polished silicon surface is typically less than 10.sup.4 per cm.sup.2 (10.sup.-4 per square micron)--many orders of magnitude less than that exhibited by most materials.
As a result, diamond film growth procedures often employ substrate preparation techniques in an attempt to increase the nucleation density to a practicable level. Such techniques typically involve introduction of surface discontinuities by scratching or abrading the surface of the substrate with a polishing or grinding material usually a diamond paste or powder. Such surface discontinuities are believed to create preferential sites for diamond crystal nucleation. Or, embedded residues from the diamond paste or powder may serve as sites at which diamond growth can occur by accumulation.
Despite such surface preparation techniques, the nucleation densities for diamond films prepared by such techniques remain low--approximately 10.sup.8 per cm.sup.2 (1 per square micron). Moreover the surface structure of these films is unpredictable, and they typically exhibit very disordered surface patterns. For these reasons such films often are not useful in many applications where diamond films are theoretically well suited.
It is thus an object of the invention to provide a method of growing quality, polycrystalline films of diamond and other materials upon foreign substrates. A further object of the invention is to provide a method of treating substrate materials so as to increase the nucleation density of films such as diamond. Another object of the invention is to provide a method of growing, on nondiamond substrates, diamond films having a regular and predictable crystal microstructure. It is also an object of the invention to provide quality diamond films in which the growth initiation sites of the film may be predetermined and specified. Other objects of the invention will be apparent upon reading the following disclosure.